<mat-form-field class="white-text" *ngFor="let select of selects;let $index = index;" class="cat_box">
    <mat-select  (selectionChange)="selectChangeTree($event)" [(value)]="select.active">
        <mat-option  value="" disabled>请选择...</mat-option>
        <mat-option  *ngFor="let item of select.tree" [value]="item">
            {{item.catName}}
        </mat-option>
    </mat-select>

</mat-form-field>